The present invention relates generally to document scanners, and more particularly to setting the scanner to calibrate the imaging elements of the scanner. In further particularity, the invention relates to scanners for large format documents, such as engineering drawings, that are scanned by moving the document past the imaging element of the scanner.
A document scanner receives light reflected from a document to convert the image on the document into a format for further processing. For example, an analog light lens scanner uses a lens to project the image onto an apparatus such as a photoreceptor to reproduce the document image through electrostatic printing. Scanners may also use digital photosensors that convert the light reflected from the document into digital electronic information. A lens may focus the document image onto the digital photosensors. Alternatively, a linear array of photosensors may extend across the entire width of the document to be scanned. The linear array of photosensors may be moved along the document, or the document may be moved past the linear array of photosensors. In certain instances, it may be possible to scan the document using digital photosensors that move in a raster format, moving the photosensors across the document in a predetermined pattern.
The imaging apparatus, whether a photoreceptor, or an array of digital photosensors (with or without a focusing lens) should be calibrated for maximum performance of the scanner in creating a faithful image or reproduction of the document. Such calibration may include ascertaining the maximum amount of light that may be received by the optical element, determining the dimensions of the documents being scanned, and determining the nature of the background of the document to be scanned.
The present invention is a method and apparatus for calibrating a document scanner.
The calibration method of the present invention includes positioning a calibration structure in a first position in which a first portion of the calibration structure is in the field of view of the optical element of the scanner, and then scanning the first portion of the calibration structure to perform a light calibration. The method also includes the step of moving a portion of a document to be scanned into the field of view of the scanner optical element, and positioning the calibration structure in a second position in which a second portion of the calibration structure is in the field of view of the optic element, and the document is in the optical path between the optical element and the second portion of the calibration structure, and then determining the width of the document. The method further includes positioning the calibration structure in a third position in which a third portion of the calibration structure is in the field of view of the optical element.
A calibration apparatus in accordance with the invention includes a substantially cylindrical casing having a longitudinal central axis and an outer surface. A first portion of the outer surface encompasses a first segment of the circumference of the outer surface, and is white. A second portion of the outer surfaces encompasses a second segment of the circumference of the outer surface of the casing, and is black. A document backer comprises a longitudinal slot through the outer surface of the casing, encompassing a third segment of the circumference of the outer surface of the casing, and a backer roller positioned in the slot. A driver is connected to the casing for selectively positioning the casing in first, second, or third rotational positions in which the first, second, or third portions of the outer surface of the cylindrical casing, respectively, face in a first direction.
A document scanner in accordance with the present invention includes an optical element that has a field of view, and a document transport mechanism for moving a document in a first direction past the optical element. The scanner additionally includes a calibration casing having an outer surface, wherein a first portion of the outer surface is a first color, and a second portion of the outer surface is a second color, contrasting with the first color. A driver is operatively connected to the casing to selectively position the first or second portion of the outer surface of the casing in the field of view of the optical element.